1. Field of the Invention
This invention relates to ethanol production from the fermentation of sucrose as it is naturally found in sugar cane. The invention relates to methods of fermenting cane pieces or particles, separation of the alcoholic yeast suspension and using said suspension to ferment again new or fresh cane pieces. This novel process whereby sucrose is extracted from cane and converted in situ in stoichiometric proportions, into ethanol, is for convenience referred to herein as "Exferm" process.
2. Description of the Prior Art
Ethanol production by fermentation is one of the oldest processes known to humankind, and has been employed principally for the elaboration of alcoholic beverages. It is said that Assyrian kings in 3500 BC had vineyards and wineries, see Hoogerheide, J. C. Chem. Tech. 7 (2) 94 (1977). The fermented beverages secured from sugar cane are usually associated with rum. The raw materials normally employed for this purpose are final or blackstrap molasses, high test molasses, virgin syrups, sugar cane juice and "panela" or the resulting solid from boiling raw juice. Rum manufacture has probably been in existence for more than 300 years and the first rum factories or distilleries were probably erected in the middle of the seventeenth century in the Caribbean islands; see, for example, Olbrich, H. Ann. Technol. Agric. 24 (3) 411-420 (1975). The process used by modern rum distilleries has not been subjected to major technical innovation in decades. This process consists basically of the following operations: (a) molasses handling, dilution, clarification and heat treatment, (b) anaerobic fermentation by a selected yeast strain, previously grown under controlled conditions, (c) yeast separation from the broth, (d) alcohol separation by distillation and eventual storage. For detailed descriptions and technical details see for example: Harrison, J. S. and Graham, J. C. J. "Yeast in Distillery Practice" in A. H. Rose and J. S. Harrison (Eds.) "The Yeasts" 3 (6) 283-348 (1970), Academic Press; Kampen, W. H. Sugar y Azucar 70 (8) 36-39, 42-43 (1975); L'Anson, J. A. P. Process Biochem. 11 (7) 35-39 (1971). In none of these references or in the related and similar technical literature is there any description of rum production directly from the fermentation of sugar cane, as the whole stack, fragments, small pieces, or a highly pulverized product. Even in very small or primitive sugar cane processing operations, there has always been the tendency to extract the juice or syrup from the solid fiber matrix. A recent article, Lipinsky, E. S. Science 199: 644-651 (1978), suggests, in general terms only, fermenting the extracted pith from cane directly with molasses. Tentscher, W., Owsianowski, R. P., Rudolph, K., and Bruschke, H., at the International Symposium on Alcohol Fuel Technology, held in Wolfburg, BRD, Nov. 21-23, 1977 (Papers 5-4, 5-5) have also suggested a process that has as an alternative approach the fermentation of crushed cane. It is noted that this is only a one step fermentation, however, and does not involve stoichiometric conversion of sucrose to ethanol from cane.
In sum, then, none of the foregoing references, nor the commercial practices known heretofore, in which molasses provides the preferred substrate for fermentation, teach the essentially stoichiometric conversion of sucrose in whole cane into ethanol by the repeated action of yeast thereon.
Accordingly, if means were provided for producing stoichiometric quantities of ethanol by fermentation of sucrose in comminuted sugar cane, the procedure would constitute a significant advance in the state of the art. If this result could be secured in a manner such that the fermentation proceeds in substantially as efficient a manner as where fermentation is effected in homogeneous liquid substrates an additionally unexpected and material advance in the relevant art would result.